SCN in aromatic compounds

Phenols and primary, secondary, and tertiary aromatic amines with free ortho- and/or /wra-positions react readily with thiocyanogen, (SCN)2. SCN enters the position para to the OH or NR2 group, or, if that is occupied, into the orfAtf-position.11,12 In the later case subsequent ring closure may be easy.14,760 For instance, / -toluidine gives 6-methylbenzo[A]thiazole-2-amine, and etyhl / -aminobenzoate gives ethyl 2-aminobenzo[Z ]thiazole-6-carboxylate. 

Although thiocyanogen does not react with benzene or naphthalene, it does react with more highly condensed aromatic compounds such as anthracene benzopyrene, etc.761 The substance may be added to a solution of thiocyanogen (for its preparation see page 104), but it is simpler to generate the thiocyanogen in situ. The (SCN)2 is produced in the reaction mixture from alkali thiocyanate and bromine or chlorine or from Cu(SCN)2. Suitable solvents for work with bromine or chlorine are acetic acid, methanol, and methyl acetate, the last two saturated with NaBr or NaCl. 

6-Isopropyl-3-methyl-4-thiocyanatophenol 13 Thymol (15 g) and NaSCN 2H20 (35 g) are dissolved in methanol (150 ml) saturated with NaBr. Bromine (20 g) in methanol (30 ml) saturated with NaBr is added to this solution at room temperature with stirring. After 30 min a six- to eight-fold amount of water is added, whereupon the product separates as an oil. This crystallizes in 2 h at 0°, is dried on porous plate, and after recrystallization with charcoal from light petroleum has m.p. 105° (yield 95 %). 

A similar reaction in methanol at 5° gives a 97% yield of p-thiocyanatoaniline.12 

The preparation of A,A-dimethyl-/ -thiocyanatoaniline, described in detail in Organic Syntheses,762 exemplifies the use of ammonium thiocyanate in glacial acetic acid. 

---